The field of art to which this invention pertains is the hydrocracking of a hydrocarbonaceous feedstock. Petroleum refiners often produce desirable products such as turbine fuel, diesel fuel and other products known as middle distillates as well as lower boiling hydrocarbonaceous liquids such as naphtha and gasoline by hydrocracking a hydrocarbon feedstock derived from crude oil, for example. Feedstocks most often subjected to hydrocracking are gas oils and heavy gas oils recovered from crude oil by distillation. A typical gas oil comprises a substantial portion of hydrocarbon components boiling above about 700xc2x0 F., usually at least about 50 percent by weight boiling above 700xc2x0 F. A typical vacuum gas oil normally has a boiling point range between about 600xc2x0 F. and about 1050xc2x0 F.
Hydrocracking is generally accomplished by contacting in a hydrocracking reaction vessel or zone the gas oil or other feedstock to be treated with a suitable hydrocracking catalyst under conditions of elevated temperature and pressure in the presence of hydrogen so as to yield a product containing a distribution of hydrocarbon products desired by the refiner. The operating conditions and the hydrocracking catalysts within a hydrocracking reactor influence the yield of the hydrocracked products.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial activities, there is always a demand for new hydrocracking methods which provide lower costs and higher liquid product yields while maintaining product quality. It is generally known that enhanced product selectivity can be achieved at lower conversion per pass through the catalytic hydrocracking zone. Low conversion per pass is generally more expensive, however, the present invention greatly improves the economic benefits of a low conversion per pass process while preserving product quality.
U.S. Pat. No. 5,720,872 (Gupta) discloses a process for hydroprocessing liquid feedstocks in two or more hydroprocessing stages which are in separate reaction vessels and wherein each reaction stage contains a bed of hydroprocessing catalyst. The liquid product from the first reaction stage is sent to a low pressure stripping stage and stripped of hydrogen sulfide, ammonia and other dissolved gases. The stripped product stream is then sent to the next downstream reaction stage, the product from which is also stripped of dissolved gases and sent to the next downstream reaction stage until the last reaction stage, the liquid product of which is stripped of dissolved gases and collected or passed on for further processing. The flow of treat gas is in a direction opposite the direction in which the reaction stages are staged for the flow of liquid. Each stripping stage is a separate stage, but all stages are contained in the same stripper vessel.
International Publication No. WO 97/38066 (PCT/US 97/04270) discloses a process for reverse staging in hydroprocessing reactor systems.
U.S. Pat. No. 3,328,290 (Hengstebeck) discloses a two-stage process for the hydrocracking of hydrocarbons in which the feed is pretreated in the first stage.
U.S. Pat. No. 5,114,562 (Haun et al) discloses a process wherein distillable petroleum streams are hydrotreated to produce a low sulfur and low aromatic product utilizing two reaction zones in series. The effluent of the first reaction zone is purged of hydrogen sulfide by hydrogen stripping and then reheated by indirect heat exchange. The second reaction zone employs a sulfur-sensitive noble metal hydrogenation catalyst.
U.S. Pat. No. 5,980,729 (Kalnes et al) discloses a hydrocracking process which utilizes a hot, high-pressure stripper.
The present invention is a catalytic hydrocracking process which provides lower costs and higher liquid product yields while reducing the production of undesirable normally gaseous hydrocarbons and maintaining product quality. The process of the present invention provides the yield advantages associated with a low conversion per pass operation without compromising unit economics. The envisioned high recycle liquid rate will reduce or eliminate the need for hydrogen quench and minimize the fresh feed pre-heat since the hot recycle liquid will provide heat. In addition, the low conversion per pass operation requires less catalyst volume.
In accordance with one embodiment of the present invention, a hydrocarbonaceous feedstock and a liquid recycle stream having a temperature greater than about 500xc2x0 F. and saturated with hydrogen, and a hydrogen-rich gas is contacted with a metal promoted hydrocracking catalyst in a hydrocracking reaction zone at elevated temperature and pressure sufficient to obtain a substantial conversion of the hydrocarbonaceous feedstock to lower boiling hydrocarbons. The resulting hot, uncooled effluent from the hydrocracking reaction zone is hydrogen stripped in a stripping zone maintained at essentially the same pressure as the hydrocracking zone with a first hydrogen-rich gaseous stream to produce a first gaseous hydrocarbonaceous stream and a first liquid hydrocarbonaceous stream. At least a portion of the first gaseous hydrocarbonaceous stream is condensed to produce a second liquid hydrocarbonaceous stream and a second hydrogen-rich gaseous stream. At least a portion of the first liquid hydrocarbonaceous stream is recycled to supply the liquid recycle stream and at least a portion of the second hydrogen-rich gaseous stream is recycled to provide at least a portion of the hydrogen supplied to the hydrocracking reaction zone. At least a portion of the second liquid hydrocarbonaceous stream is recovered and separated to produce desired hydrocarbonaceous product streams. At least another portion of the second liquid hydrocarbonaceous stream is introduced into a hydrogenation zone and the resulting effluent is introduced into the stripping zone.
In accordance with one embodiment the present invention relates to a process for hydrocracking a hydrocarbonaceous feedstock to produce lower boiling hydrocarbonaceous compounds which process comprises: (a) contacting the hydrocarbonaceous feedstock, a liquid recycle stream having a temperature greater than about 500xc2x0 F. and saturated with hydrogen, and added hydrogen with a metal promoted hydrocracking catalyst in a hydrocracking zone at elevated temperature and pressure sufficient to obtain a substantial conversion to lower boiling hydrocarbons; (b) stripping the uncooled hydrocarbon effluent from the hydrocracking zone in a hot stripping zone maintained at essentially the same pressure as the hydrocracking zone with a first hydrogen-rich gaseous stream to produce a first gaseous hydrocarbonaceous stream and a first liquid hydrocarbonaceous stream; (c) condensing at least a portion of the first gaseous hydrocarbonaceous stream and separating the same into a second liquid hydrocarbonaceous stream and a second hydrogen-rich gaseous stream; (d) recycling at least a portion of the first liquid hydrocarbonaceous stream to supply at least a portion of the liquid recycle stream in step (a); (e) recycling at least a portion of the second hydrogen-rich gaseous stream from step (c) to supply at least a portion of the added hydrogen in step (a) and at least a portion of the first hydrogen-rich gaseous stream in step (b); (f) introducing at least a portion of the second liquid hydrocarbonaceous stream and hydrogen into a hydrogenation zone; (g) directly introducing the effluent from the hydrogenation zone into the stripping zone as reflux; and (h) recovering at least another portion of the second liquid hydrocarbonaceous stream.
Other embodiments of the present invention encompass further details such as types and descriptions of feedstocks, hydrocracking catalysts, hydrogenation catalysts and preferred operating conditions including temperatures and pressures, all of which are hereinafter disclosed in the following discussion of each of these facets of the invention.
The drawing is a simplified process flow diagram of a preferred embodiment of the present invention. The drawing is intended to be schematically illustrative of the present invention and not be a limitation thereof.